The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The problem of storing fuel (hydrogen carrier or H2) has still not been satisfactorily solved for the broad use of fuel cells, for example, in motor vehicles. Different methods for the storage of H2 are known:
Pressure storage of H2 in pressure vessels at up to 700 bar;
Pressureless storage as liquid H2 in cryogenic dewars at temperatures of below −253° C.;
Storage in metals or metal alloys that form thermo-reversible intercalation compounds (metallic hydrides) with H2;
Storage in form of hydrogen-rich organic compounds, such as, for example, methane, methanol, benzene, etc., which are subjected to a reformation reaction in order to release H2;
Storage in form of H2O, which is decomposed into H2 with suitable metals (for example, Li, Na, K, Mg, etc.);
Storage in form of salt-like metal hydrides (for example, NaH, LiH, etc.), which are decomposed into H2 with H2O;
Storage in form of complex metal hydrides, for example, LiAlH4, NaBH4, etc., which are decomposed into H2 with H2O.
Most of the aforementioned methods are technically or energetically very complex, and allow only the storage of very low quantities of H2, or are not controllable from the point of view of safety for broader applications.
From DE 601 08 744 T2 is known a process for producing hydrogen for a fuel cell. The process steps comprise the conversion of a metal hydride, which is different from NaAlH4, with at least one alcohol, wherein hydrogen is formed, and the hydrogen is fed into a hydrogen chamber of a fuel cell. Hydrides of the metals Li, Na, K, Mg, Ca, Zr and Ti are mentioned as particularly suitable hydrides. Compounds having the formula M2v,M3wHy are presented as particularly suitable complex hydrides, wherein M2 is a metal selected from among the group consisting of Li, Na, K, Mg, Ca, Fe and Zr; M3 is selected from among the group consisting of Al, B, Be and Ti.
One of the disadvantages of H2 storage with the aid of metal hydrides is that metal hydrides or complex metal hydrides are solids as a rule. These solids are difficult to store, deliver and meter. They are frequently insoluble. Fueling with these substances represents already a not inconsiderable problem, in particular in motor vehicles. The delivery of metal hydride from the storage tank to a hydrogen generator that may be necessary in the motor vehicle is also difficult. A further disadvantage is that the degradation products or hydrolysis products of metal hydrides are generally highly corrosive brines, in particular LiOH, NaOH, KOH, Ca(OH)2, etc. These degradation products are highly corrosive and harmful to the environment. These substances are also questionable with regard to their environmental safety because unintentional release and therefore the formation of degradation products can always be expected when these substances are utilized in large scale.